The present invention relates to a method for forming a resist pattern and a manufacturing method of a thin-film element wherein resist patterns for patterning thin-films are formed by using the above-mentioned forming method.
Fabrication of a thin-film element such as a thin-film magnetic head includes several thin-film patterning processes such as milling or dry-etching processes or lift off processes. Each of the patterning processes starts from a process of forming a photoresist pattern.
There are various structures for the photoresist pattern. Recently, a photoresist pattern with two-layer structure having reverse-trapezoid cross section or T-shaped cross section has received attention.
FIG. 1 illustrates a conventional photoresist pattern with the two-layer structure having T-shaped cross-section.
As shown in the figure, this photoresist structure has a two-layer photoresist structure formed by multi-layering a polymethyl glutarimide (PMGI) layer 11 and a resist layer 12 on a substrate 10. The resist layer 12 protrudes toward the lateral direction and thus has a larger width than the PMGI layer 11. As will be noted form the figure, the conventional two-layer photoresist structure has the T-shaped cross section in which overhang portions 12a protrude and extend horizontally from the resist layer 12.
However, if the photoresist pattern with the horizontally extending overhang portions 12a is used for the milling process, material removed from the milled layer will be re-deposited on the side surface of the PMGI layer 11 and on the bottom surface of the resist layer 12. These re-deposited materials will finally remain as burrs or micro projections. Furthermore, if the photoresist pattern with the horizontally extending overhang portions 12a is used for the lift off process, material for forming the patterned layer will be deposited on undercut areas positioned below the overhang portions 12a and thus precise and correct pattern cannot be obtained. The above-mentioned tendency becomes remarkable when the milling process or the sputtering process is performed by leaning and rotating the substrate causing the rate of fabricating defectives to increase and the yield in manufacturing thin-film elements to become worse.
Japanese unexamined patent publication No.10-261208 discloses a manufacturing method of a magnetoresistive effect (MR) head for decreasing the rate of fabricating defectives and for improving the yield in manufacturing thin-film elements. This known method uses a two-layer structure pattern with a lower layer and an upper layer for the lift off process. The upper layer has a width larger than that of the lower layer and has the negative mechanical stress, and thus the upper layer bends so that its center portion upwardly projects and its end portions curve toward the substrate.
It is therefore an object of the present invention to provide a method for forming a resist pattern and a manufacturing method of a thin-film element, whereby the rate of fabricating defectives (rejection rate) can be extremely decreased and the yield in manufacturing the thin-film elements can be remarkably improved by executing a simple process.
According to the present invention, a method for forming a resist pattern includes a step of forming a two layer structure resist pattern with a T-shaped cross section, which consists of a lower layer and an upper layer with overhang portions, and a step of heat-treating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward.
Also, according to the present invention, a method for manufacturing a thin-film element includes a step of forming a two layer structure resist pattern with a T-shaped cross section, which consists of a lower layer and an upper layer with overhang portions, a step of heat-treating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward, and a step of patterning a thin-film using the heat-treated two layer structure resist pattern.
According to the present invention, further, a method for manufacturing a thin-film element includes a step of depositing a layer to be patterned on a substrate, a step of forming a two layer structure resist pattern with a T-shaped cross section on the layer to be patterned, which consists of a lower layer and an upper layer with overhang portions, a step of heat-treating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward, and a step of dry-etching the layer to be patterned, using the heat-treated two layer structure resist pattern.
According to the present invention, still further, a method for manufacturing a thin-film element includes a step of forming a two layer structure resist pattern with a T-shaped cross section on a substrate, which consists of a lower layer and an upper layer with overhang portions, a step of heat-treating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward, and a step of depositing a layer to be patterned, using the heat-treated two layer structure resist pattern.
According to the present invention, also, a method for manufacturing a thin-film element includes a step of depositing a first layer to be patterned on a substrate, a step of forming a two layer structure resist pattern with a T-shaped cross section on the first layer to be patterned, which consists of a lower layer and an upper layer with overhang portions, a step of heat-treating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward, a step of dry-etching the first layer to be patterned, using the heat-treated two layer structure resist pattern, and a step of depositing a second layer to be patterned, using the heat-treated two layer structure resist pattern.
After a two-layer structure resist pattern with a T-shaped cross section is formed, the two-layer structure resist pattern is heat-treated so that overhang portions of its upper layer incline downward. Thus, when milling patterning is executed, no removed material by milling is re-deposited on the bottom surface of the upper layer of the two layer structure resist pattern and on the side surfaces of the lower layer of the resist pattern. Therefore, no burr will remain on the patterned layer and a precise pattern of satisfactory quality can be provided. When lift off patterning is executed, material of the patterning layer is never deposited on the substrate surface below the overhang portions (undercut regions) of the two-layer structure resist pattern. Thus, a precise pattern of satisfactory quality can be obtained. As a result, the rejection rate is extremely reduced and the yield rate is remarkably improved. Particularly, according to the present invention, since such resist pattern can be obtained only by performing a heat treatment process that is simple and easily controllable, the manufacturing process is never complicated.
It is preferred that the heat-treating step is executed before or during the patterning step, the dry-etching step or the depositing step. In the latter case, it is more preferred that controlling cooling temperature during the patterning step, the dry-etching step or the depositing step performs the heat-treating step. Since no additional process for heat treatment is needed, the resist pattern forming process or the manufacturing process of a thin-film element can be more simplified.
It is also preferred that the lower layer is made of a resin material, and wherein the upper layer is made of a resist material. The resin material may be polymethyl glutarimide (PMGI) or PMGI with dye additives.
It is preferred that the heat-treating step includes heating the formed two layer structure resist pattern so that the overhang portions of the upper layer incline downward by 10 to 25 degrees.
It is also preferred that the heat-treating step includes heating the formed two layer structure resist pattern at a temperature within a range of 70 to 130xc2x0 C.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.